Event: Make focus re-triggering not focus the original element back

mgol · web-flow · commit dbcffb396c2d · 2020-12-07T20:28:44.000+01:00
If during a focus handler another focus event is triggered: ```js elem1.on( "focus", function() { elem2.trigger( "focus" ); } ); ``` due to their synchronous nature everywhere outside of IE the hack added in gh-4279 to leverage native events causes the native `.focus()` method to be called last for the initial element, making it steal the focus back. Since the native method is already being called in `leverageNative`, we can skip that final call. This aligns with changes to the `_default` method for the `click` event that were added when `leverageNative` was introduced there. A side effect of this change is that now `focusin` will only propagate to the document for the last focused element. This is a change in behavior but it also aligns us better with how this works with native methods. Fixes gh-4382 Closes gh-4813 Ref gh-4279
diff --git a/src/event.js b/src/event.js
@@ -746,6 +746,12 @@ jQuery.each( { focus: "focusin", blur: "focusout" }, function( type, delegateTyp
 			return true;
 		},
 
+		// Suppress native focus or blur as it's already being fired
+		// in leverageNative.
+		_default: function() {
+			return true;
+		},
+
 		delegateType: delegateType
 	};
 } );
diff --git a/test/unit/event.js b/test/unit/event.js
@@ -3291,6 +3291,40 @@ QUnit.test( "native-backed events preserve trigger data (gh-1741, gh-4139)", fun
 	}, 50 );
 } );
 
+QUnit.test( "focus change during a focus handler (gh-4382)", function( assert ) {
+	assert.expect( 2 );
+
+	var done = assert.async(),
+		select = jQuery( "<select><option selected='selected'>A</option></select>" ),
+		button = jQuery( "<button>Focus target</button>" );
+
+	jQuery( "#qunit-fixture" )
+		.append( select )
+		.append( button );
+
+	select.on( "focus", function() {
+		button.trigger( "focus" );
+	} );
+
+	jQuery( document ).on( "focusin.focusTests", function( ev ) {
+		// Support: IE 11+
+		// In IE focus is async so focusin on document is fired multiple times,
+		// for each of the elements. In other browsers it's fired just once, for
+		// the last one.
+		if ( ev.target === button[ 0 ] ) {
+			assert.ok( true, "focusin propagated to document from the button" );
+		}
+	} );
+
+	select.trigger( "focus" );
+
+	setTimeout( function() {
+		assert.strictEqual( document.activeElement, button[ 0 ], "Focus redirect worked" );
+		jQuery( document ).off( ".focusTests" );
+		done();
+	} );
+} );
+
 // TODO replace with an adaptation of
 // https://github.com/jquery/jquery/pull/1367/files#diff-a215316abbaabdf71857809e8673ea28R2464
 ( function() {
